# What is Needle: Definition and 65 Discussions

A sewing needle, used for hand-sewing, is a long slender tool with a pointed tip at one end and a hole (or eye) at the other. The earliest needles were made of bone or wood; modern needles are manufactured from high carbon steel wire and are nickel- or 18K gold-plated for corrosion resistance. High quality embroidery needles are plated with two-thirds platinum and one-third titanium alloy. Traditionally, needles have been kept in needle books or needlecases which have become objects of adornment. Sewing needles may also be kept in an étui, a small box that held needles and other items such as scissors, pencils and tweezers.

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1. ### B Can a Compass Needle be Magnetized to Any Horizontal Direction?

A compass needle can be magnetized to point to the north. Am I correct in thinking that the needle could have been magnetized to point to any other horizontal direction?
2. M

### B What if a needle hits Jupiter at nearly speed of light?

This is much like the "grain of sand" at near speed of light hiting Earth, but now targeting Jupiter with a needle! What if... Any way, which is the correct way to analyze this kind of scenarios? For example, I think than being the speed of the needle near c, is nonsense to think about the...
3. ### B Stability of Droplet Climbing on a Needle with Varying Contact Angle

Let's say we are pushing water down a needle, the contact angle between the needle and the water is ##\mathrm{45°}##. For simplicity let's assume there is no gravity. As the water is initially moving down in the left image, the angle ##\theta=\mathrm{45°}## and the surface of the water is a...
4. ### Work done on a magnetic dipole (compass needle rotating)

So this is a sketch I made of the situation and this is my approach my approach is incorrect , and Idon't seem to find the mistake , maybe B*p isn't correct. Any ideas?
5. ### Graph of torque against displacement of galvanometer needle

My guess is (c) since the rest of the options do not make sense to me but I am not sure about the shape of the graph. Is (c) the correct answer? If yes, how to know whether the shape will be like in the option (straight line then curve downwards) or other shape like straight line only (like y =...
6. ### Thrust Ball bearing and Needle Bearing

Hello all friends, My questions about the these two types of bearings. I know that what is purpose of usage. But I don't know where can I use them. If someone knows information about that, please inform me. Thanks you all.
7. ### Does a Voltmeter's needle jump?

I think Voltmeter's needle will not jump in both situations. But the answer is yes. I am going to use this to explain why. The reasons to create the voltage are by - The changing by time of Magnetic field - The move of the object in magnetic field In both situations, they are not occur so I...
8. ### I Probability involving a needle

My approach to this problem is a little laborious, it involves three coordinates, probably it is right, but tiring and extensive beyond what the question wanted. Be the origin in the rectangle middle. It would be like: imagine a rectangle with opposite sides L and R with length l, so to find...
9. ### I Is my solution to Buffon's needle OK?

Buffon's needle was presented as a problem in David Griffiths' "Introduction to Quantum Mechanics". In the book, a needle is of length l is dropped randomly on a sheet of ruled paper with the lines of the paper also a distance l apart. It is required to find the probability of the needle...
10. ### I Why does this needle get an E field while this disk gets a D field?

So I'm reviewing old lectures to prepare for an exam soon. This is about polarization. E fields, D Fields, etc. My professor labeled this diagram like so. The figures my professor drew are cavities in a dielectric if you can't read her handwriting. However, I can't seem to figure out why the...
11. ### Surface Tension of needle on water

I attempted the question but it was wrong... I don't understand where i went wrong my working seems logical, can someone please help. When a needle is gently placed on the surface of still water (γ = 0.0730 N.m-1) it can be supported by surface tension if the mass of the needle is small enough...
12. U

### How rubbing a needle on a magnet affects its polarity

Homework Statement It is known that when rubbing a needle on a magnet, the needle will become magnetized. If you rub the needle on the north side of the magnet, will it point differently than if you rubbed it on the south side of the magnet? Does it matter what direction you rub the needle...
13. ### How do I properly mount a needle bearing for a trike swing arm?

Hi, I am have been trying to figure out the correct way to mount a needle bearing. I have previously worked with ball bearings. Here is the application: The needle bearing will be pivot point of a swing arm of a trike. Another will form the central pivot point that breaks the vehicle from...
14. ### Mathematical problem about Buffon's Needle

Buffon's Needle A floor is ruled with equally spaced parallel lines a distance D apart. A needle of length L is dropped at random on the floor. It is assumed that L no more than D. What is the probability that the needle will intersect one of the lines? This problem is known as Buffon’s needle...
15. ### A What is orientation of a needle shaped spacecraft?

this is a small part of a problem on tidal forces and I wasn't sure what the question asks as it seems to me that more information is needed. Am I right or is there something I am missing? the question goes as: "A spacecraft approaches a neutron star of radius 10 km and mass 1.5 times mass...
16. ### [Mechanics of Solid] Friction on a needle inserted in tissue

Hello , I'm trying to model the forces on a needle being inserted in a tissue. Needle tip penetrates the tissue surface and as it moves through the tissue, it experiences friction from needle-tissue interaction. Friction arises from the pressure exerted by surrounding tissue as it grips the...
17. ### Discovering Earth's Direction with Magnetic Needle Compass

Hello, How to perform and know north south from magnetic needle compass?? as in this picture it show North + south = south + north so, how to find Earth direction??
18. ### Electric field between a needle and a plate

http://i66.tinypic.com/2yts08m.jpg I was doing an experiment in which i have a needle perpendicular to a metal plate. I run 210kV between them. I want to find out the electric field between the two, and I also want to know the electric al field density throught the metal plate? Pls help. I...
19. ### Alignment of the compass needle

If a compass is placed above a current carrying wire, why does the compass needle align itself in the direction of the magnetic field produced by the wire?
20. ### Why Does a Compass Needle Deflect Between Opposing Currents?

hi, i know this question is a bit unnecessary but i just want to know if i got my concept right so, here's the question if you have a compass pointing northwards placed between two parallel wires carrying opposite current, does the needle deflect? my answer is the needle won't deflect since the...
21. ### Hypodermic Needle Fluid Dynamics

A hypodermic syringe contains a medicine with the density of water (figure below). The barrel of the syringe has a cross-sectional area of 2.18 10-5 m2. In the absence of a force on the plunger, the pressure everywhere is 1.00 atm. A force of magnitude 1.78 N is exerted on the plunger, making...
22. ### About probability of crossing a circle circumference by a needle

Buffon`s needle problem described the probability of crossing a set of parallel lines with a known distance between them by a needle of a known length. What is the probability of crossing a circumference of a circle with a known radius by a needle of a known length? I feel that a simple answer...
23. ### Linear Charge Distribution on a Needle?

http://www.colorado.edu/physics/phys3320/phys3320_sp12/AJPPapers/AJP_E&MPapers_030612/Griffiths_ConductingNeedle.pdf I was reading this paper, and was confused by a result in section 2-A. (Heck they even mention they weren't expecting it themselves). The purpose of the paper is to find the...
24. ### Why does a greased needle float on water?

So I read that if you put grease on a needle it will float on water . Why does this happen?
25. ### Compass needle, magnetic field and current

Homework Statement Eric looks at his compass to check the direction to north. At a point two (2.0) meters below Eric, a cable is drawn from south to north and the current running through the cable is 50 Amperes. This current makes the compass needle turn wrong. How big is the angle deviation if...
26. ### Moment of Inertia Compass Needle

Homework Statement You place a magnetic compass on a horizontal surface, allow the needle to settle, and then give the compass a gentle wiggle to cause the needle to oscillate about its equilibrium position. The oscillation frequency is 0.321 Hz. Earth's magnetic field at the location of the...
27. ### Battery alone deflects compass needle?

Homework Statement I'm an introductory electromagnetism course and in lab we were observing how an electric current could deflect a compass needle. however, i also noticed that the batter itself (with no wire attached, so no current) could also deflect the needle. (for ex, if you brought the...
28. ### Sizing Needle Valves for Air Flow | 0.025 m^3/s

I am trying to size a needle valve to make sure that it can allow the required flow rate at the fully open position (0.025 m^3/s). For a given Cv you should be able to calculate the maximum flow rate through the needle valve provided that you know the temperature of the gas and the pressure drop...
29. ### Radon transform, Buffon's needle and Integral geometry

In all the literature that I have seen it is mentioned that these two are "branches" of integral geometry, but no where I can see the exact connection since one is connected with probability and the other is an integral. I have seen this, but it is not clear...
30. ### Direction of Compass Needle near a Solenoid

A compass is placed near a solenoid. It is closer to the North pole generated by the coil. The magnetic north is 90 deg relative to the compass and the solenoid. The strength of the solenoid is equal to the strength of the magnetic north. In which direction will the compass needle point?
31. ### Probability density of a needle

A needle on a broken car speedometer is free to swing and bounces perfectly off the pins at either end, so if you give it a flick it is equally likely to come at rest at any angle between 0 and pi. If the needle has a length r, what's the probability density ρ(x) of the x-coordinate of the...
32. ### Magnetic needle inside a solenoid

What will happen If I place a magnetic needle inside a solenoid, I mean will the South Pole of the needle be directed towards the South Pole of the solenoid since it is north from inside and the same way regarding the North Pole
33. ### Flipping the polarity of a compass needle. Why does this work?

Awhile back I had been messing around with batteries, copper wiring, compasses and small neodymium magnets; during this time I figured out how to flip the polarity of a compass needle. The most reliable way was to hold the two magnets above the compass needle and force, as best I could, the two...
34. ### Archived Some question about the Maxwell needle method experiment.

Homework Statement 1)How do we obtain the formula of torsional rigidity ,c=∏nr^4/(2L) ?From experiment? then how do the ∏ come from? How do they know the n here is the rigidity modulus? Why it is not the young's modulus? 2)Is Maxwell needle method same as the torsional pendulum? Both can be...
35. ### Math in Maxwell needle method- the formula the moment of inertia

[b]1. Homework Statement [ How do I get I1( the moment of inertia of the picture b) ?is just a math problem but really no idea. Homework Equations I=mr^2 The Attempt at a Solution maybe centre of mass . Guide will do . please help , thank
36. ### Impulse problem about a medical biopsy needle.

Homework Statement Physicians perform needle biopsies to sample tissue from internal organs. A spring-loaded gun shoots a hollow needle into the tissue; extracting the needle brings out the tissue core. A particular device uses 8.4 needles that take 81 to stop in the tissue, which exerts a...
37. ### Static-E Attraction on Knitting Needle

https://www.youtube.com/watch?v=qHrBhgwq__Q&feature=player_detailpage Don Pettit, unfortunately, narrates, but doesn't explain much. The main needle is Teflon and the other needle by the injection of the water droplets (seen near the end of the vid) is Nylon. The site asks about the choice of...
38. ### Torque experienced by compass needle

The torque experienced by the compass needle is m X B , m being the magnetic moment of the compass/magnet and B being the Earth's magnetic field. The magnetic moment is along the axis pointing from South to North and the magnetic field will depend on where the compass is on the surface of the...
39. ### Needle in Die Breaking: Causes & Fixes

Hola Regarding the cold heading process I have a question and would appreciate an answer a lot. The wire, from which is bolt made, is alloy-steel but the machine is old. I have been seeing many times breakage of needle inside the die and I figured out what was the cause, I even fixed it on my...
40. ### Polyethylene Plug Style Needle Closure Autosampler Shell Vial

I have a question about https://www.amazon.com/dp/B002RS5IKA/?tag=pfamazon01-20 product. It is an autosampler shell vial with a polyethylene plug style needle closure. Does anyone know whether the plug on this vial will be resealable? In other words, will it be able to withstand multiple...
41. ### Needle probability distribution problem

Homework Statement part a(complete) The needle on a broken car speedometer is free to swing, and bounces perfectly off the pins at either end, so that if you give it a flick it is equally likely to come to rest at any angle between 0 and \pi. part b(attempting) We consider the same...
42. ### Magnetic moment of compass needle?

What would be a typical value of the magnetic moment of a compass needle (in SI units)? Thanks :-)
43. ### Rotational Inertia of compass needle

Homework Statement A small compass needle is situated in a uniform magnetic field. When displaced from its stable equilibrium position through a small angle and then released, it oscillates with a frequency of 5 Hz. A millijoule of work is needed to twist the compass needle round through...
44. ### How high should the bottle be placed above the needle?

Homework Statement A patient is to be given a blood transfusion. The blood is to flow through a tube from a raised bottle to a needle inserted in the vein. The inside diameter of the 3.82 cm long needle is 0.393 mm and the required flow rate is 3.88 cm3 of blood per minute. How high should...
45. ### Current in a wire and compass needle

Homework Statement A compass needle points 19.1 degrees E of N outdoors. However, when it is placed 9.80 cm to the east of a vertical wire inside a building, it points 55.7 degrees E of N. What is the magnitude of the current in the wire? The Earth's field there is 4.80×10-5 T and is...
46. ### Dip Needle Compass vs. Normal Compass

Why does one "dips" down and the other rotates?
47. ### Calculating h for Blood Transfusion Needle

Homework Statement A patient is to be given a blood transfusion. If the inside diameter of the 4.0 cm long needle is 0.40 mm, the blood pressure in the arm is 2400 Pa, and the required flow is 4.0 cm³/min, how high h should the bottle be placed? (ρ = 1050 kg/m³, η =0.0040 Pa·s)...
48. ### Needle which is almost touching a pane of glass

I am a little confused by movement. It is difficult to explain, but here goes. Say I have a needle which is almost touching a pane of glass, so close if fact that the smallest movement toward the pane would result in the needle touching it. My confusion is, if the needle has to move to touch the...
49. ### Half Life of radioactive needle

Homework Statement A radioactive needle contains 222 Rn (t1/2=3.83 d) in secular equilibrium with 226 Ra(t1/2=1600 a). How long does is it required for 222 Rn to decay to half of its original activity?Homework Equations A(t) = -\frac{dN(t)}{dt} = \lambda N(t) The Attempt at a Solution...
50. ### Needle suspended from string - dipole moment?

Homework Statement A needle suspended from a string hangs horizontally. The electrical field at the needle's location is horizontal with magnitude 3.7 x 10^3 N/C and it's at an angle of 30 degrees with the needle. There is no net electrical force acting on the needle, but the string exerts...